I've sold 2 Macbooks and a Macbook Air in the last couple of years and I won't even list mine on the FS/FT secton here anymore. I sold one on Craigslist and the rest went on Ebay. I do get a low of lowballers on CL, but nothing compared to the FS/FT section here. The last Macbook I listed was a mint black MB for $550, I recieved an inbox full of $350-$400 offers here and ended up listing it on Ebay and ended up getting $750, which more than made up for the fees.
I think a lot of this has to do with the forum members actually know what a used Mac is really worth. There are enough idiots on Ebay that buy into the Mac hype that they will pay ridiculous prices for them. You will have good luck on Ebay if you have very good feedback, that makes a lot of difference in the end price.